As to manufacturing a capacitor to be provided to a DRAM and a ferroelectric memory, various kinds of material and film forming methods have been suggested. In addition, the film forming methods practically utilized now are mainly a sol-gel method and a sputtering method. However, for recent scale up of the integration degree of a memory, it becomes difficult for the methods to achieve thinning of a film thickness and step coverage. Consequently, a film forming method by means of a MOCVD (Metal Organic Chemical Vapor Deposition) method has recently come to attract attention.
However, when a PZT (Pb(Zr, Ti)O3) film is formed by the MOCVD method, its composition, especially, its ratio of the numbers between A-site atoms and B-site atoms (hereinafter, also referred to as A/B ratio) tends to fluctuate. When the A/B ratio fluctuates, the electric characteristics of a ferroelectric capacitor (switching charge amount Qsw and leak current) largely fluctuate. In general, it is considered to be preferable to suppress the fluctuation range of the electric characteristics to be within ±0.5%. Moreover, in a conventional ferroelectric capacitor with a PZT film, as its A/B ratio becomes higher, its switching charge amount Qsw becomes larger and its leak current becomes larger.
For this reason, in the conventional ferroelectric capacitor, though, in order to obtain a large switching charge amount Qsw, the A/B ratio is intended to be set high within an allowable range of the leak current, the A/B ratio may practically fluctuate beyond a predicted range, which may cause the leak current to exceed the allowable range. Accordingly, since it is required to set the A/B ratio while preliminarily estimating the fluctuation range of the leak current to be larger, it is currently difficult to obtain a large switching charge amount Qsw.
Patent Document 1
Japanese Patent No. 3385889